One technique for encoding time series signals such as speech signals and acoustic signals with a small number of bits is code excited linear prediction (CELP), which is used in cell phones and the like. CS-ACELP and 3GPP AMR (refer to non-patent literature 1, for example) defined in ITU-T G.729 are typical CELP techniques.
For encoding and decoding in a predetermined time interval (frame, subframe, etc.), typical CELP techniques use the linear sum of adaptive signal components obtained by delaying one or more excitation signals at a point preceding the predetermined time interval in accordance with a pitch period and a pulse sequence from a fixed codebook, as an excitation signal of the predetermined time interval. The pitch period and pulse sequence are encoded, and a code including the code corresponding to the pitch period and the code corresponding to the pulse sequence is generated.